1. Field of the Invention
The present invention relates to an apparatus for, and a method of, printing a pattern on the inside radius of a curved substrate. More particularly, the present invention relates to an apparatus for, and a method of, printing a precise pattern on the inside radius of a curved substrate by the pivotal movement of a pendulum across the surface of a screen which is capable of receiving and transferring a printing ink to a surface of the curved substrate.
2. Discussion of the Related Art
Various methods of printing patterns on flat substrates have long been known. Methods of printing patterns on the outside radius of a curved surface are also known. It has been difficult, however, to find a reliable means to print complex, precise patterns on the inside surface, or inside radius, of a curved substrate. Such printing means would be particularly applicable to curved substrates, such as plastics or glass, which could be used as automotive glazings.
Examples of conventional printing apparati and methods of printing are disclosed in, for example:
U.S. Pat. No. 6,041,702 teaches a screen printing apparatus for screen printing on curved objects with relatively large radii of curvature, but does not teach a method or apparatus to print on the inside curve of such an object.
U.S. Pat. No. 5,743,182 teaches a stencil printing method and apparatus for printing directly on a curved surface, but again, teaches only printing on the outside surface of an object, and a moving diaphragm, rather than a pendulum, effects the printing of a pattern on the substrate.
U.S. Pat. No. 5,339,732 teaches a machine for printing on the outside of containers through use of a squeegee device, however, it does not teach printing on the inside radius of a curved surface, nor does it teach a pendulum printing apparatus.
U.S. Pat. No. 5,170,703 teaches a machine for printing a curved surface, but does not teach printing on the inside radius of a curved surface, use of a non-stationary squeegee or use of a printing screen conformable to the substrate on which the pattern is to be printed.
U.S. Pat. No. 4,381,706 teaches a screen for printing on curved surfaces comprising a flexible frame which allows certain segments of the frame to flex into a shape complementary with the shape of the article to be printed. The patent does not teach, however, a pendulum-mounted squeegee for printing, nor does it teach printing on the inside radius of a curved surface.
International Application Publication No. WO00/78520, filed Jun. 22, 2000, teaches a process for manufacturing molded plastic curved automotive window panels in which a blackout and decorative border is printed on the perimeter of the panel with ink. To print on the curved surface of the window panel a squeegee wiper is mounted on a pendulum arm to provide a constant angle position as the screen is wiped by a swinging movement of the pendulum. A hinged frame allows it to roughly assume the same of the panel curvature.
Accordingly, it would be advantageous to have a method of printing on the inside surface of a curved substrate, and to provide a relatively simple apparatus capable of doing so. It would be particularly advantageous to have such an apparatus and method of printing which is adaptable to high-volume manufacturing of, for example, curved, plastic, or glass automotive glazings.
The present invention addresses the problem of printing a variety of precise patterns on a substrate material having a curved shape. This capability is particularly useful where first printing such a pattern and then attempting to bend the flat substrate material could cause deformation or marring of the printed pattern. The present invention is useful where the substrate is a plastic material, and is particularly useful where the substrate is an injection molded cylindrical polycarbonate material, such as can be used for an automotive glazing for windows.
More specifically, the apparatus and method of the present invention may be employed to print a pattern on the inside radius of a curved substrate where the radius of curvature is approximately 20-80 inches, measured from the pivotal mounting point of the pendulum, which is a component of the present invention, to the uppermost surface of the substrate on which a pattern is to be printed.
Another component of the apparatus of the present invention is the screen and the screen mounting frame which, prior to deflection, are in a generally flat, horizontal position above the curved substrate. The substrate is supported by a support member, itself having a curved surface, which, in general, conforms to the shape of the curved substrate. While in the flat, horizontal position, a flood bar is actuated, and moves across the screen, ensuring that the desired portion of the screen is uniformly covered with ink. Various printing inks suitable for different applications may be used in conjunction with the present invention.
The screen and screen mounting frame move, typically, in a downward direction, so that the screen substantially conforms with the shape of the curved substrate which has been placed beneath the screen. Once properly conformed to the shape of the curved substrate, a means for spreading printing ink across the now-curved screen moves across the screen. The means attached to a pendulum capable of pivotal movement is actuated and moves arcuately across the screen, with sufficient pressure being applied to the spreading means to transfer the ink through the mesh of the screen onto the inside radius of the curved substrate. Preferably, the spreading means is a squeegee, the material for the spreading edge of such squeegee being any suitable material such as a polyurethane material which is well-known in the art for squeegee construction.
The length of the pendulum arm may be fixed or preferably the length of the pendulum arm may be adjustable so that it is capable of printing on curved substrates having radii of curvature between 20 and 80 inches, although, preferably between 38 and 60 inches.
Similarly, a number of different support members having differing shapes and curvatures may be utilized to accommodate substrates having different curvatures. This may be acceptable if only a small number of different curvatures is desired. If, however, a significant number of parts having different curvatures is envisioned, or rapid changeover from one curvature to another is anticipated, a single support member having substantial capability to adjust its shape might be desirable. Accordingly, both fixed and adjustable support members are disclosed herein.